Corin is a pirate with a secret. No one on the ship knew that she is really a mermaid. Humans rarely look upon the outwardly non-humans too kindly and Corin loves being a pirate almost as much as she loves the ocean...and Jacintha, her captain. When a mission to steal from a nobleman goes awry and Jacintha gets hurt, Corin uses her mermaid nature to save her. Revealing herself is dangerous, especially since Jacintha is her captain, but she can't let her die.
Saving Jacintha is the best thing that happens to Corin. Jacintha doesn't hate Corin for being a mermaid. In fact, she's thrilled that Corin is a mermaid. Even more so, Jacintha is mutually attracted to her. Corin is a mermaid and a pirate, and now love is her next great adventure.